In a small saucepan, combine orange juice, lemon juice, orange zest, lemon zest, honey, Dijon mustard, and garlic. Bring to a simmer over medium heat and cook, stirring occasionally, until reduced to a glossy, syrupy glaze that coats the back of a spoon, 5–7 minutes. Off the heat, whisk in the butter until smooth; keep warm.
Pat the salmon fillets dry. Season both sides with the kosher salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat until shimmering. Add the salmon, skin-side down, and cook without moving until the skin is crisp and the fillets are mostly opaque, 4–5 minutes. Flip and cook until just translucent at the center, 1–2 minutes more.
Reduce the heat to low. Pour about half of the warm citrus glaze into the skillet and turn the salmon to coat, letting the glaze bubble and lacquer the fish, 30–60 seconds.
Transfer the salmon to plates and spoon the remaining glaze over the top. Let rest 2 minutes and serve.